外部連結
- RFC 3851: Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification
- RFC 5751: Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message Specification (Draft Tracker（页面存档备份，存于互联网档案馆）)
- Microsoft Exchange Server: Understanding S/MIME（页面存档备份，存于互联网档案馆） – high-level overview
- How to secure email using S/MIME standard
Free S/MIME providers
- MeSign 密信（页面存档备份，存于互联网档案馆） - Completely Free certificates 永久免费证书
